LAS VEGAS — The costs and benefits of rooftop solar electricity in Western states emerged as a key topic during an annual green power conference hosted Monday by U.S. Sen. Harry Reid in Las Vegas.

President Barack Obama was expected to keynote the close of the eighth National Clean Energy Summit at the Mandalay Bay resort.

Obama is using an event that Reid has nurtured during his time as Democratic leader of the Senate to announce new executive actions and other efforts aimed at making it easier for homeowners and businesses to invest in green energy improvements.

Reid opened the conference highlighting a local utility’s plan to build a 15 megawatt solar generation project on 80 acres west of Las Vegas. It will serve the Valley Electric Association, and company chief Tom Husted said it could help lower electricity prices for about 25,000 customers in Nevada and California.

The debate about costs to consumers installing home rooftop solar panels and to utilities that control the electric grid in sunny states like Nevada, Arizona, California, New Mexico and Utah provided a point-counterpoint discussion between Charles Cicchetti of the Pacific Economics Group, speaking for consumers, and Lisa Wood of the Edison Foundation, representing utilities.

“It’s a misconception that rooftop solar users don’t need the grid,” Wood said. She called it only fair that customers continue to pay to maintain the transmission system from which they draw electricity during peak use times and at night.

The misconception, Cicchetti said, is that consumers are required to buy power from the utilities. The bigger danger to the companies, he said, would be for rooftop solar users to become so alienated that they find ways to store electricity collected during the day and withdraw from the grid altogether.

The question hits home in Nevada, where the dominant utility, publicly traded NV Energy, reported last week that it hit a preset statewide cap of 235 megawatts on the amount of rooftop solar power it will buy back from customers.